As is well known in the air conditioning art, and more particularly those employing hermetic refrigeration systems, maximum efficiency of an evaporator is attained by maintaining the refrigerant stream leaving the evaporator in a saturated gaseous state so that the entire heat transfer surface of the evaporator is subjected to heat absorption by vaporization. With this ideal condition, therefore, the refrigerant absorbs latent heat in the evaporator and no sensible heat to raise its temperature following vaporization with the result that the maximum available refrigerating affect is attained. It has been general practice in the refrigeration industry to size evaporator coils with an amount of surface and pressure drop to assure that the refrigerant leaving the evaporator is in an expanded and superheated gaseous state.
The condenser, on the other hand, is designed to provide totally liquid phase refrigerant to the expansion or capillary valve, which, as is well known cannot tolerate any significant amount of refrigerant gas. Consequently, the refrigerant must be totally condensed to a liquid phase in the condenser.
Conventional heat pump refrigeration systems of the type to which this invention particularly relates comprises indoor and outdoor coils or heat exchangers connected to a closed refrigerant circuit. Refrigerant is circulated through the coils by a compressor which pumps the compressed refrigerant gas through the coil where it is condensed and passes through a means for expansion, such as a capillary tube or expansion valve, to the other coil for evaporation. The system includes suitable change-over valve mechanisms for reversing the function of the indoor and outdoor heat exchangers permitting the indoor exchanger to function as an evaporator for summertime cooling or as a condenser for wintertime heating, the upper coil performing the opposite function.
One of the shortcomings of the prior art heat pump refrigeration systems of the type described above is their incapability of the heat exchangers to operate efficiently both as evaporators and condensers. This is especially true since it takes a greater pressure drop through the condenser to change the high pressure gas to a high pressure liquid than it does for the evaporator to change low pressure liquid to a low pressure gas. Accordingly in heat pump or reverse cycle refrigeration systems when the coils designed to operate as evaporators and condensers are reversed in the refrigeration cycle they are inefficient.